1. Field of the Invention
The present invention relates to optoelectronic assemblies, sub-assemblies and components, and more particularly to high tolerance components used to align optical fibers in single fiber and multi-fiber optical fiber connections.
2. Description of Related Art
Optical fiber based communication channels are the system of choice in many defense and commercial applications because of their high performance and small size. Particularly, fiber optics have “proved-in” in long distance applications, such as city-to-city and continent-to-continent communication spans, because of lower costs of electrical-to-optical-to-electrical (E-O-E) conversion components, fiber amplifiers, and fiber cables relative to pure electrical systems using coaxial copper cable that do not require E-O-E. These long haul fiber systems can have hundreds of kilometers of fiber between terminals.
Shorter distance systems typically have only a few tens of kilometers of fiber between terminals, and very short reach (VSR) systems have only a few tens of meters of fiber between terminals. Although fiber links for telecom and datacom in metro, access and premise areas are short as compared to long haul links, there are a great many of them. The number of components required in the deployment of fiber for these types of applications is large. In these short distance systems, fiber optics “prove-in” is very sensitive to the cost of E-O-E terminal conversion devices and supporting circuitry, as well as any passive and active optoelectronic devices and equipment linked between terminal ends. Consequently, for optoelectronic active and passive assemblies, sub-assemblies and components to “prove-in” in short distance and VSR systems, their average sell prices must be lowered. Lowering of the average sell prices will help stimulate the unit volume necessary to justify investment in high speed manufacturing technologies.
A significant element of the cost of both active and passive fiber components and connectorized cable is the fiber connector itself. Ferrules and associated means for aligning them (e.g., split sleeves for single fiber connection, ground pins for multi-fiber connections) dominate the cost of current fiber connectors. The alignment components are normally required to align fibers to active and passive devices and to align two fibers for demountable connection and for splicing. Precision alignment of two polished fiber ends is needed to ensure that overall optical loss in a fiber link is equal or less than the specified optical connector loss budget for a system. For single-mode telecommunication-grade fiber, this typically corresponds to connector fiber alignment tolerances that are less than 1000 nm. Connectors, in both parallel fiber and single fiber links, operating at multi-gigabit rates must be assembled with subcomponents fabricated with sub micron precision. As if producing parts with such precision levels were not challenging enough, for the resulting end product to be economical it must be done in a fully automated, very high-speed process.
Current connectors have not changed in basic design for more than 20 years. The basic designs of ferrules, split sleeves and grooves date back to the 1970's. Conventional ferrules are solid cylinders with a hole centered on the axis of the cylinder into which a fiber, typically 0.125 mm in diameter, is inserted and affixed. The outside diameter of the cylinder is typically 2.5 mm, and its length is typically 10 mm. For the most part, products on the market today incorporate these same designs but are made from different materials and made by different manufacturing methods. For single fiber-to-fiber applications, ferrules are typically made from machined-formed metal blanks or zirconia ceramics. In a multi-step process, zirconia blanks are molded to approximate sizes, and then the blanks are machined and grinded to the desired size and tolerances. For multi-fiber applications, ferrules are typically made from thermoset plastic impregnated with silica spheres. The silica spheres result in a thermal expansion coefficient of the composite plastic-glass material system closer to that of silica fibers than that of pure plastic. It is generally accepted that current fiber connectors cost too much to manufacture. The cost of manufacturing fiber connectors must decrease if fiber optic is to be the communication media of choice for short haul and VSR applications.
Stamping processes have been deployed in manufacturing processes for mass-producing parts at low cost. Stamping is a fabrication process that presses a work piece, such as a metal strip, between a die set assembly into a predetermined shape or pattern. The die set assembly can perform various stamping operations on the work piece, such as cutting, forming (e.g., punching, drawing, bending, flanging and hemming), and forging (e.g., coining). Generally, forming is referenced to a stamping operation that does not substantially alter the thickness of a work piece, while forging is referenced to a stamping operation that substantially alters the thickness of the work piece. Compared to the processes of machining molded zirconia blanks or molded silica impregnated thermoset plastic, stamping is a relatively faster process.
Stamping processes, however, have not been effective in producing parts With acceptable tolerances for optoelectronic components. U.S. Pat. No. 4,458,985 to Balliet et al. is directed to an optical fiber connector. Balliet describes in a cursory manner that some of the connector components can be produced by a coining or stamping process (e.g., col. 3, lines 20-21, 55-57). However, Balliet does not provide an enabling disclosure of such stamping process, let alone an enabling disclosure of a stamping process for producing parts within 1000 nm.
In our pending U.S. patent application Ser. No. [Not Yet Available], entitled “Stamping System for Manufacturing High Tolerance Parts,” filed on Jul. 15, 2003, which is incorporated by reference in its entirety, we describe a system and process for stamping parts, such as optoelectronic assemblies, sub-assemblies and components, having tolerances within 1000 nm. FIG. 1 is a schematic drawing illustrating a system 10 for stamping optoelectronic components having tolerances below 1,000 nm. The stamping system 10 includes, in part, a stamping press 20, one or a progression of stamping stations 25, and an interface system 35. Each stamping station 25 can include tools, such as a punch and die for performing a specific stamping operation on a work piece, sensors for in-line metrology and/or tool protection, and other equipment, such as a welder. The stamping stations 25 include a novel structure for guiding the punch in substantial alignment with the die with tight tolerances. Also, the stamping stations 25 are designed to minimize the number of moving components involved in the support structure in guiding the punch to the die. The stamping press 20 powers the progression of stamping stations 25. The interface system 35 facilitates coupling the force of the press 20 with the punch but structurally decoupling the press 20 from the punch. The interface system 35 also allows isolation of each stamping station so that operation at one station does not affect operation at another station.
This precision stamping process is capable of producing parts with a “six sigma” geometrical tolerance band of 1,000 nm. Statistically, this means that at most only 3.4 parts per million will not meet dimensional requirements defined by the 1,000 nm tolerance band. For a normal distribution, to achieve a six sigma process, the standard deviation of the complete process must be less than or equal to 83 nm [(1000 nm/2)/6=83 nm], provided the mean of the process remains constant. In practice, an allowance must be made to accommodate shifts in the process mean. For the case where the shift in process mean of ±1.5*sigma is accommodated, the maximum standard deviation is reduced to 67 nm [(1000 nm/2)/7.5=67 nm]. Again, assuming normal statistics, to achieve this in a multistage process with n precision stages, each of the n-stages must have sigma/n^0.5. So if n=4 in this example, then sigma (per stage) is less than or equal to 33 nm.
It is therefore desirable to have precision optoelectronic assemblies, sub-assemblies and components that are designed for manufacturability in a high-speed stamping process capable of producing parts having tolerances within 1,000 nanometers. It is also desirable to have precision optoelectronic assemblies, sub-assemblies and components that are designed for manufacturability in the stamping system described in our pending U.S. patent application Ser. No. [NOT YET AVAILABLE].